计算机样条的数学形式——逐段圆曲线插值

所谓的计算机样条,是应用计算机绘图软件在已知结点上生成的一条可控形状的光滑平面曲线。计算机样条的数学形式是一组递推公式,避免了线性方程组的求解。由于圆曲线的双值性,使用解析法时需借助图解法,虽不很方便但可获得更高的精度。

3D Simulation of Two-bar Warp-knitted Structures

In this study, 3D computer modeling of simple warp-knitted structures is achieved based on 3D model of warp-knitted loops. Firstly, according to the studying on the geometric structure of warp-knitted loops, Goktepe＇s 3D solid yarn model is developed, and the dimensions of the warp-knitted loops are obtained; then 3D models of stitch defined by eleven given points and in-lay defined by five given points are built with the method of Non-Uniform Rational B-Spline （NURBS） curves and surfaces. Secondly, according to the chain notations of warp-knitted structures, the loop＇s shape can be decided, and with the 3D models the loops can be connected freely and smoothly in some special warp-knitted structures, such as miss-lapping and two- course in-lay. At last, with the tools of Visual C ＋＋ and OpenGL, computer 3D simulation of two-bar warp-knitted fabrics is successfully realized, taking the factor of fabric light and materials into 3D structural model.

Multi-modality liver image registration based on multilevel B-splines free-form deformation and L-BFGS optimal algorithm

A new coarse-to-fine strategy was proposed for nonrigid registration of computed tomography(CT) and magnetic resonance(MR) images of a liver.This hierarchical framework consisted of an affine transformation and a B-splines free-form deformation(FFD).The affine transformation performed a rough registration targeting the mismatch between the CT and MR images.The B-splines FFD transformation performed a finer registration by correcting local motion deformation.In the registration algorithm,the normalized mutual information(NMI) was used as similarity measure,and the limited memory Broyden-Fletcher- Goldfarb-Shannon(L-BFGS) optimization method was applied for optimization process.The algorithm was applied to the fully automated registration of liver CT and MR images in three subjects.The results demonstrate that the proposed method not only significantly improves the registration accuracy but also reduces the running time,which is effective and efficient for nonrigid registration.

A Computer Modeling of the China Central Television Headquarters in Beijing

This paper deals with the computer modeling of structures starting from a point cloud. The CCTV （China Central Television） tower headquarters is the case for study because the shape of this building is non-stellar, concave and multi-connected. It is composed of sowns and chains. The sown is the representation of a horizontal plane formed by dense points. The chain is a planar path modeled by rare points. The CCTV structure is defined only by the three orthogonal Cartesian coordinates of the points. The proposed computer modeling uses a sequence of procedures and the desired outputted 3D model is consistent. The first procedure is devoted to attributing points to their voxel and to estimating three values needed afterwards. The second procedure is devoted to analyzing clusters vertically and horizontally, to preliminarily distinguishing chains from sowns and to generating relational matching. The third procedure is devoted to building closed paths between all chains and all their projections on sowns. The fourth procedure is devoted to connecting points with triangles. The fifth procedure, still being implemented, is devoted to interpolating triangles with triangular splines. The results show it is possible to achieve the 3D model using the above mentioned procedures. These procedures are written, implemented and tested and they form a library of people＇s own software. The code is written using Matlab. It is not possible to obtain the required 3D model if the procedures are applied in the wrong order or one step is skipped. To conclude, it is possible to obtain the computer model of the CCTV using the provided sequence of procedures.